The biophysical properties of gap junction channels in embryonic cells will be studied, and mechanisms responsible for changes in these properties will be sought. The decrease in junctional conductance (gj) produced by low intracellular pH (pHi) will be studied: pHi will be measured and correlated with gj and parameters of voltage dependence to establish the pK for block of the channel, the pK of the voltage dependent gate, and the approximate number of titratable sites involved in each process. Group specific protein reagents will be used to identify peptide residues involved in the control of gj by pH and voltage. Noise analysis of currents through voltage clamped gap junctions will be used to estimate single channel conductance and to detect changes caused by pHi, transjunctional voltage and protein reagents.